The invention generally concerns a theft protection system for a recessed installation unit and more particularly to such an arrangement for sounding an alarm when unauthorized movement of the installation unit is detected as well as for restraining the unauthorized removal of the unit from the vehicle.
A theft protection system is disclosed by German Published, Unexamined Patent Application No. (DE-OS) 34 43 650 in which an installation unit, which has first been released by a suitable tool which forces it out of its retention means, can be easily stolen by unauthorized persons despite the alarm which is set off because of a lack of further protection against removal.
On the basis of the above noted deficiencies, it has been proposed in German Published, Unexamined Patent Application No. (DE-OS) 35 45 233 that the alarm should be initiated as soon as parts of the frame of the installation unit have been removed if, for example, an unauthorized person attempts to get to the mechanical retention arrangement hidden below the covered frame parts in order to release this retention arrangement.
It has also been disclosed to initiate an alarm in the case of unauthorized opening or removal of a movable cap or covering provided for camouflage in front of an installation unit as set forth in German Published, Unexamined Patent Application Nos. (DE-OS) 35 28 016 and (DE-OS) 35 37 371. In these latter theft protection systems, therefore, the relative motion, between two parts for the purpose of switch actuation or circuit interruption to initiate the alarm was transferred to other movable (fitted) parts, in contrast to the generic arrangement described above wherein the installation unit itself as the moving part which is used to initiate the alarm.
Although this measure does remove the disadvantage associated with the criticism mentioned above, it only permits the protection for the installation unit to be effective until the removal of the cover or cap. If the alarm initiated has been cancelled, after 30 seconds to suit the legal regulations, the installation unit is only protected by the particular mechanical retention means. These, however, are also generally accessible from the front of the installation unit and can be released by appropriate simple tools.
Another, purely mechanical theft protection system for installation units of the type under discussion is disclosed by German Published, Unexamined Patent Application No. (DE-OS) 36 18 681 in which an installation unit is fixed in its installation shaft by a tensionable tension element fastened to the back of the unit. The armored tension element is only accessible to unauthorized persons by very great effort. In comparison with the conventional installation arrangements, however, comprehensive removal work is necessary for any repairs which may be necessary to the installation unit because, among other things, part of the screw protecting the tension element must be drilled out every time. A guide and armoring for the tension element by a tube is proposed particularly for the case of factory (mass-produced) installation of the theft prevention system last mentioned.
In connection with the protection of remotely unlockable engine hoods on motor vehicles, mechanical directly acting protection systems are disclosed by German Published, Unexamined Patent Application No. (DE-OS) 23 14 957, and remotely controllable tension element protection systems actuated by external force are disclosed by German Published, Unexamined Patent Application No. (DE-OS) 21 16 448, which can prevent the unauthorized displacement of the engine hood remote unlocking cable run, by unauthorized persons. However, reference to a theft protection system for an installation unit cannot be found in the foregoing patent applications.
Accordingly, an object of the present invention is to provide a theft protection system in which an alarm is initiated by the relative motion between the installation unit, or its retention arrangement, and the installation passage, while ensuring simple installation and removal of the installation unit by authorized persons from the insertion opening of the installation shaft.
The preferred embodiments of the invention achieve these and other objects by utilizing a mechanical protection stop which permits limited movement of the installation unit from an installed position before actuating an alarm, the mechanical protection stop working in cooperation with a retention arrangement for preventing removal of the unit from the vehicle by unauthorized persons.
Because the installation unit in its installation passage, is always movable with a limited distance, i.e. even in the protected condition, a similarly movable Protection stop, ensuring the protecting limitation of this distance, makes displacement of the retention arrangement possible in the installation shaft which is inaccessible when the installation unit is protected, and permits simple installation and removal of the installation unit by authorized persons because of the limited mobility of the protection stop.
The retention arrangement includes cable connections necessary, according to a preferred embodiment of the present invention, which do not provide any problems because these must, in any event, be long enough to permit complete withdrawal of the installation unit from the installation passage and complete cabling before insertion of the installation unit.
The usual sliding guides in the installation passage and on the installation unit can be retained unaltered. All that is required are one or more points of action on the installation unit for a return force clamping the installation unit in its installation position.
In accordance with a first embodiment, the retention arrangement is biased to draw the installation unit towards the installation position by a tension element, the return force is then rationally provided if the usual retention engagement lugs, etc. are omitted so that the installation unit can be secured in its installation position even in the case of road irregularities and vehicle accelerations. The disappearance of the usual retention engagement lugs on the side of the installation unit does have the advantage that it is no longer necessary to provide an opening on the front of the installation unit or caps for covering this opening.
In accordance with the teaching of a further embodiment of the present invention, which does not provide for any return force, the usual retention engagement lugs are provided in addition to the movable protection stop. However, the protection stop alone always undertakes the actual mechanical theft protection.
The theft protection for the installation unit obtainable by bringing the protection stop into its protection location is very large, independent of its type of engagement on a tension element or on the casing of the installation unit, because there is no possibility for unauthorized persons to interfere with it from the front of the installation unit. The limited mobility of the protection stop is preferably associated with the use of a key, a mechanical or remotely controlled motion actuated by external force also being possible.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.